The South American sea lion (Otaria flavescens, formerly Otaria byronia), also called the southern sea lion and the Patagonian sea lion, is a sea lion found on the Chilean, Ecuador, Peruvian, Uruguayan, Argentine and Southern Brazilian coasts. It is the only member of the genus Otaria. Its scientific name was subject to controversy, with some taxonomists referring to it as Otaria flavescens and others referring to it as Otaria byronia. The former eventually won out,[2] although that may still be overturned.[3] Locally, it is known by several names, most commonly lobo marino (sea wolf) and león marino (sea lion).

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The South American sea lion is perhaps the archetypal sea lion in appearance. Males have a very large head with a well-developed mane, making them the most lionesque of the eared seals. They are twice the weight of females.[4] Both males and females are orange or brown coloured with upturned snouts. Pups are born greyish orange ventrally and black dorsally and moult into a more chocolate colour.

The South American sea lion's size and weight can vary considerably. Adult males can grow over 2.73 m (9 ft) and weigh up to 350 kg (770 lb).[5] Adult females grow up to 1.8–2 m (6–7 ft) and weigh about half the weight of the males, around 150 kg (330 lb). This species is even more sexually dimorphic than the other sea lions.[6]

The South American sea lion is found along the coasts and offshore islands of South America, from Peru south to Chile in the Pacific and then north to southern Brazil in the Atlantic.[7] It travels north during the winter and spring and goes south to breed.[7] Notable breeding colonies include Lobos Island, Uruguay; Peninsula Valdes, Argentina; Beagle Channel, and the Falkland Islands. Some individuals wander as far north as southern Ecuador, although apparently they never bred there.

South American sea lions prefer to breed on beaches made of sand, but will breed on gravel, rocky, or pebble beaches, as well.[7] They can also be seen on flat, rocky cliffs with tidepools.[7] Sea lion colonies tend to be small and scattered, especially on rocky beaches.[7] The colonies make spaces between each individual when the weather is warm and sunny.[7] They can also be found in marinas and wharves, but do not breed there.

Mating occurs between August and December, and the pups are born between December and February. Males arrive first to establish and defend territories, but then switch to defending females when they arrive.[6] A male aggressively herds females in his territory and defends both from neighbors and intruders.[6] On rocky beaches, males establish territories where females go to cool off and keep them until estrus.[7] On cobble or sandy beaches, males have territories near the surf and monopolize females trying to get access to the sea.[7] The number of actual fights between males depends on the number of females in heat.[6] The earlier a male arrives at the site, the longer his tenure will be and the more copulations he will achieve.[6] Males are usually able to keep around three females in their harems, but some have as many as 18.[6]

Male with harem

Female sea lion and pup

During the breeding season, males that fail to secure territories and harems, most often subadults, will cause group raids in an attempt to change the status quo and gain access to the females.[11] Group raids are more common on sandy beaches than rocky ones.[11] These raids cause chaos in the breeding harems, often splitting mothers from their young. The resident males try to fight off the raiders and keep all the females in their territorial boundaries. Raiders are often unsuccessful in securing a female, but some are able to capture some females or even stay in the breeding area with one or more females.[11] Sometimes, an invading male abducts pups, possibly as an attempt to control the females.[11] They also take pups as substitutes for mature females.[12] Subadults herd their captured pups and prevent them from escaping, much like adult males do to females.[12] A pup may be mounted by its abductor, but intromission does not occur.[12] While abducting pups does not give males immediate reproductive benefits, these males may gain experience in controlling females.[12] Pups are sometimes severely injured or killed during abductions.[11][12]

Sea lion mothers remain with their newborn pups for nearly a week before making a routine of taking three-day foraging trips and coming back to nurse the pups.[6][7] They act aggressively to other females that come close to their pups, as well as alien pups that try to get milk from them.[13] Pups first enter the water at about four weeks and are weaned at about 12 months. This is normally when the mother gives birth to a new pup. Pups gradually spend more time in the nearshore surf and develop swimming skills.[7]

South American sea lions are observed to make various vocalizations and calls which differ between sexes and ages.[14] Adult males make high-pitched calls during aggressive interactions,[14] barks when establishing territories,[14] growls when interacting with females,[14] and exhalations after antagonistic encounters.[14] Females with pups make a mother primary call when interacting with their pups,[14] and grunts during aggressive encounters with other females.[14] Pups make pup primary calls.[14] Some of those vocalizations and acoustic features may support individuality.[14]

The Moche people of ancient Peru worshipped the sea and its animals. They often depicted South American sea lions in their art.[15] Two statues of this species are the symbol of the city of Mar del Plata.

Indigenous peoples of South America exploited this species for millennia and by Europeans around the 16th century.[16] The hunting has since gone down and the species is no longer threatened. The species is protected in most of its range.[1] Numerous reserves and protected areas at rookeries and haul-out sites exist for the sea lions.[1] Despite this, protection regulations are not effectively enforced in much of animals' range.[1]

The overall population of sea lions is considered stable; the estimate is 265,000 animals. They are increasing in Argentine Patagonia, but are declining in Chile and Uruguay.[1] Many sea lions of the Peruvian population died in the 1997/1998 el Niño.[1] They still are killed due to their habits of stealing fish and damaging fishing nets.[1] Sea lions in the port of Mar del Plata have been found with toxic chemicals and heavy metals in their systems.[17]